1318 2005-05-10 10:49:52 +0000 Comparing durations for equality 2005-09-29 10:48:14 +0000 1 1 1 Unclassified XPath / XQuery / XSLT Functions and Operators 1.0 Last Call drafts PC Windows XP CLOSED FIXED P2 normal --- 1 mike ashok.malhotra public-qt-comments oldest_to_newest 3565 0 mike 2005-05-10 10:49:52 +0000 ACTION: A-252-01 - Michael Kay will file a separate LC comment on "Specify an equality comparison for xs:duration values" and proposing a comparison mechanism. Bug 1208 should be dependent on the new bug, and when we resolve the new bug we will revisit 1208. We should define an equality comparison for xs:duration values. (a) There's no good reason not to. Although ordering of durations is problematical, there's no problem defining equality. Admittedly there is more than one possible definition, but that's true of many of our data types. (b) Not having an equality operation for durations causes implementation difficulties with other operations such as distinct-values(), deep-equal(), and (in XSLT) sorting and grouping. For example, distinct-values() treats all durations as distinct from each other, which makes it hard to come up with a suitable hashing function; similarly, deep-equal() has to search a document to arbitrary depth, because if it contains a duration anywhere then it is not deep-equal to any other document, not even itself. The proposed definition is that two durations $d1 and $d2 are equal if and only if xdt:dayTimeDuration($d1) eq xdt:dayTimeDuration($d2) and xdt:yearMonthDuration($d1) eq xdt:yearMonthDuration($d2). To implement this: (a) in the language books, add two lines to the operator mapping table in B.2: A eq B | xs:duration | xs:duration | op:duration-equal(A, B) | xs:boolean A ne B | xs:duration | xs:duration | fn:not(op:duration-equal(A, B)) | xs:boolean (b) Add a new function to F+O: 10.4.x op:duration-equal op:duration-equal( $arg1 as xs:duration, $arg2 as xs:duration) as xs:boolean Summary: Returns true if and only if $arg1 is equal to $arg2. Returns false otherwise. This function backs up the "eq" and "ne" operators on xs:duration values. The function returns true if xdt:dayTimeDuration($arg1) eq xdt:dayTimeDuration($arg2) and xdt:yearMonthDuration($arg1) eq xdt:yearMonthDuration($arg2); otherwise it return false. Examples: xs:duration("P1Y") eq xs:duration("P12M") returns true. xs:duration("PT24H") eq xs:duration("P1D") returns true. xs:duration("P1Y") eq xs:duration("P365D") returns false. Michael Kay 3418 1 mike 2005-05-10 10:55:51 +0000 In F+O, Appendix D.6 should also be removed, as should the paragraph in 10.2 "No operators are defined on the [XML Schema Part 2: Datatypes Second Edition] datatype xs:duration. Appendix D.6 Working With xs:duration Values discusses how to work with xs:duration values.". In 10.4, change "For this reason, no functions are defined on xs:duration." to "For this reason, no ordering functions are defined on xs:duration." 2989 2 ashok.malhotra 2005-05-31 16:34:46 +0000 The joint WGs agreed to add the operator op:duration-equal and make the changes suggested by Michael Kay in the comments attached to this note to the F&O and the language book. See minutes on joint WG meeting 5-16-2005. Ashok Malhotra